package org.bouncycastle.asn1.x9;

import java.math.BigInteger;

import org.bouncycastle.asn1.ASN1EncodableVector;
import org.bouncycastle.asn1.ASN1OctetString;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.asn1.DERBitString;
import org.bouncycastle.asn1.DEREncodable;
import org.bouncycastle.asn1.DERInteger;
import org.bouncycastle.asn1.DERObject;
import org.bouncycastle.asn1.DERSequence;
import org.bouncycastle.math.ec.ECCurve;

/**
 * ASN.1 def for Elliptic-Curve Curve structure. See X9.62, for further details.
 */
public class X9Curve implements DEREncodable, X9ObjectIdentifiers {
    private ECCurve curve;
    private byte[] seed;

    public X9Curve(ECCurve curve) {
        this.curve = curve;
        this.seed = null;
    }

    public X9Curve(ECCurve curve, byte[] seed) {
        this.curve = curve;
        this.seed = seed;
    }

    public X9Curve(X9FieldID fieldID, ASN1Sequence seq) {
        if (fieldID.getIdentifier().equals(prime_field)) {
            BigInteger q = ((DERInteger) fieldID.getParameters()).getValue();
            X9FieldElement x9A = new X9FieldElement(true, q, (ASN1OctetString) seq.getObjectAt(0));
            X9FieldElement x9B = new X9FieldElement(true, q, (ASN1OctetString) seq.getObjectAt(1));
            curve = new ECCurve.Fp(q, x9A.getValue().toBigInteger(), x9B.getValue().toBigInteger());
        } else {
            throw new RuntimeException("not implemented");
        }

        if (seq.size() == 3) {
            seed = ((DERBitString) seq.getObjectAt(2)).getBytes();
        }
    }

    public ECCurve getCurve() {
        return curve;
    }

    public byte[] getSeed() {
        return seed;
    }

    /**
     * Produce an object suitable for an ASN1OutputStream.
     * 
     * <pre>
     *  Curve ::= SEQUENCE {
     *      a               FieldElement,
     *      b               FieldElement,
     *      seed            BIT STRING      OPTIONAL
     *  }
     * </pre>
     */
    public DERObject getDERObject() {
        ASN1EncodableVector v = new ASN1EncodableVector();

        v.add(new X9FieldElement(curve.getA()).getDERObject());
        v.add(new X9FieldElement(curve.getB()).getDERObject());

        if (seed != null) {
            v.add(new DERBitString(seed));
        }

        return new DERSequence(v);
    }
}
